Needless to say, exploring the ruins of the old Ukrainian town doesn't pose an immediate health risk. While there are certain areas of the exclusion zone worth giving a wide berth (see: the power plant and Red Forest), the vast majority of the zone (9 percent of it, or thereabouts) contain no more radioactivity than places of elevated natural radiation like Colorado and Cornwall, said Jim Smith, a professor of environmental science at the University of Portsmouth, to IFLScience.
"Natural radiation worldwide varies – if you're living at high altitudes, you get more cosmic radiation," said Smith. "For most of the exclusion zone, the doses that you would get living there are within that range of variability of radiation doses worldwide."
To break it down into numbers: Many of the liquidators (or first responders) who were called in to clean up the leak in 1986 were exposed to doses of around 800,000 to 160,000 microsieverts (µSv)*. That is extremely high and more than enough to cause vomiting, internal bleeding, and death within weeks of exposure. But the average annual dosage above natural background across much of the zone today is only around 1,000 µSv*.This is lower than the instant radiation you would receive if you were to go in for a whole-body CT scan (10,000 µSv*). [*Figures are based on calculations published by the BBC.]
That's most of the exclusion zone but not all. There are various "hotspots" that contain significantly higher rates of background radiation. Take, for example, the Red Forest, where you would receive an approximate dose rate of 350,000 µSv a year.